Customarily, spring assemblies for bottoms and backs of furniture are comprised of wire grid frames--a rigid bottom frame of relatively heavy gauge wire and a rigid top frame of lighter gauge wire between which are secured tapered helical coils, the top loops of which are of larger diameter than the bottom loops. The respective frames are structured to provide seats for the tops and bottom loops. Heretofore, the top loops have either been fixed to the wires of the seats with fastening elements, for example, clips and/or twists of wire or structured to be interlocked with each other without the aid of fastening elements. The bottom loops, however, are attached by means of fastening elements. The present invention has for its purpose to provide an improved structure wherein both the bottom and top loops are structured to be interengaged with the wires of the seat without the aid of fastening elements and in such a way as to facilitate assembly and immobilize the springs relative to the frames.